Environmental constraints on Didymosphenia geminata occurrence and bloom formation in Canadian Rocky Mountain lotic systems

The first documented bloom of Didymosphenia geminata in Alberta occurred in 2003, and subsequent field investigations revealed that D. geminata was present in the periphyton of a number of lotic systems, yet did not always form blooms. We sampled 76 sites in Canadian Rocky Mountain National Parks, chosen to provide ranges in exposure to D. geminata propagules and environmental conditions thought to affect D. geminata growth and bloom formation. Generalized linear models were then used to determine environmental constraints on habitat suitability and requirements for blooming and nonblooming populations across the landscape. Didymosphenia geminata was detected at 88% of sites, and of those, 34% had blooms, defined as visible mats of D. geminata stalks. Didymosphenia geminata cell abundance was significantly negatively related to stream velocity, stream order, and total phosphorus concentration, yet there was no significant relationship between D. geminata blooms and any of environmental variables measured....